Over the weekend media outlets received an e-mail from a woman claiming to be “the hunter of bus drivers”. The messages – not yet verified as authentic by police – said the murders were revenge for female passengers being allegedly abused by night-shift drivers.

It read: “I myself and other women have suffered in silence but we can’t stay quiet anymore.”

On Wednesday a woman – with a blonde wig or dyed hair – shot the first driver in the head with a pistol, Associated Press reported. The next day the apparent same woman repeated the attack, this time reportedly saying before pulling the trigger: “You guys think you’re real bad, don’t you?”

The Diario de Juarez newspaper reported the killer did not rob the victims.

According to the alleged killer’s message, many women became victims of sexual violence when they travelled by bus to work in factories across the border in Texas.

Arturo Sandoval, spokesman for the Chihuahua state prosecutors’ office, said the vigilante claim is considered one of the working hypotheses in the crimes.